The 840 Pro is stunning. Samsung have created a completely in-house package including both the controller and their own new 21nm toggle mode NAND. On release (Oct '12) this was the fastest performing deep queue depth consumer grade SSD available. Fast forward six months (Apr '13) and the 840 Pro still holds both the random read/write deep queue depth speed records of 384 MB/s and 326 MB/s, impressive considering how fast the SSD space tends to move. There are no obvious weaknesses, in-fact the 840 pro takes first place in nearly all of the speed categories and is only seriously rivalled by one drive, the OCZ Vector. To conclude, in terms of both outright performance, particularly server orientated, and value for money the 256GB and 128GB 840 Pros are amongst the top handful of drives currently available. [Jun '13SSDrivePro]

The Evo is remarkable in that, like the Sandisk Extreme II, it features a second level cache. For the 250 GB Evo this consists of a 3 GB Turbowrite cache (TWC) which is a block of high speed Flash Memory. When the TWC is exhausted write speeds drop by approximately 50% but that won't often happen under typical consumer workloads. In terms of raw performance, even with its cache, the Evo still isn't the fastest drive. With a real world speed index reading of 439 MB/s the EVO is however, within reach of the two speed leaders (Vector and 850 Pro). At a price point of $130 the Evo is around 30% cheaper making it the best value for money SSDs I have seen in 2014. Comparing the Evo and the Sandisk Ultra Plus shows that the Evo is the winner but the Sandisk may be a viable alternative thanks to its cache-free, and therefore more consistent performance during extended writes. [Aug '14SSDrivePro]